Wheeled carriages for supporting a patient in a substantially horizontal position are well known in the art and a representative example of an early version of such a device is illustrated in Dr. Homer H. Stryker's U.S. Pat. No. 3,304,116 reference to which is incorporated herein. Dr. Stryker's innovative wheeled carriage included a fifth wheel which is raisable and lowerable by an attendant directly manually manipulating the wheel support frame oriented beneath the patient supporting portion of the wheeled carriage. The fifth wheel is positioned at substantially the center of the undercarriage such that usually the rear castered wheels and the fifth wheel support the carriage when the fifth wheel is deployed. However, the front castered wheels and the fifth wheel may also support a patient on the wheeled carriage depending on the position of the patient. Therefore, the wheeled carriage of U.S. Pat. No. 3,304,116 can teeter between the front wheels and the rear wheels when a patient is being moved thereon with the fifth wheel deployed.
An example of a maneuverable hospital cart having a power source and a retractable drive wheel located toward the center of the cart is set forth in U.S. Pat. No. 5,083,625 to Bleicher. The cart of Bleicher includes a joystick for operating a power system to move the cart in a selected direction. The support for the fifth wheel is rotatable, thus enabling the joystick to select any direction, including sideways, for movement of the cart.
U.S. Pat. No. 5,337,845 to Foster et al discloses a care cart capable of docking with a hospital bed and including a joystick type potentiometer for controlling the speed and direction of the bed when the cart is docked thereto. The handle includes a button that enables the driving wheel to activate when selected. The joystick is connected to a pulse modulation controller circuit which is in turn connected to a motor/gear box for driving the cart. Gas springs are actuated by the bed when the motorized transport apparatus and bed are docked together to exert a downward force on the drive wheel to reduce slipping thereof during use. An electronic fuel gauge monitors the battery life of DC batteries located on board the cart. A DC battery charger on board the cart recharges the batteries when the cart is plugged into an AC wall outlet.
U.S. Pat. No. 6,256,812 to Bartow issued Jul. 10, 2001 discloses a wheeled carriage having an auxiliary wheel. The carriage includes a control pedal and a shaft. The shaft connects to a cam arrangement for moving the auxiliary wheel between first and second predetermined positions and a neutral position.
Accordingly, it is an object of this invention to provide an improved auxiliary wheel that prevents teetering of the wheeled carriage when the floor is not level. Such a result can be obtained by an auxiliary wheel spring support secured to one of the end frame members and extending at a substantially horizontal angle and biasing the auxiliary wheel downwardly to prevent teetering when the floor under the center of the wheeled carriage is higher relative to the floor at the respective ends of the wheeled carriage.
Another preferred object of the invention is to provide an improved drive handle that operates an auxiliary drive wheel to move the wheeled carriage in opposing directions corresponding to forward and rearward directions with respect to the length of the wheeled carriage. The drive handle, an auxiliary wheel drive power circuit and an electrical decision/drive circuit can operate to provide simple control requiring little strength by an operator for moving the wheeled carriage.
Another preferred object of the invention is to enable the drive handle to be used for power control during driving of the wheeled carriage when the auxiliary wheel is lowered and to be used for manual moving of the wheeled carriage when the auxiliary wheel is in a retracted position.
Another preferred object of the invention is to motion safety sensors for disabling driving of the auxiliary wheel unless one of the motion safety sensors is grasped by an operator.
Another preferred object of the invention is to provide improved operation of the power assisted wheeled carriage by using the auxiliary wheel power drive circuit to charge batteries of the wheeled carriage when the power drive circuit is connected to a standard AC electrical outlet and to provide battery power when AC power is not available.
Another preferred object of the invention is a decision/drive circuit that authorizes driving of the auxiliary wheel only when certain conditions, such as the brake being released and the auxiliary wheel being in lowered position are present. The decision/drive circuit ensures smooth driving of the auxiliary wheel when the carriage begins moving, thereby avoiding a jerking motion.
Another preferred embodiment of the invention is a timeout subroutine for preventing driving of the auxiliary wheel when the motion safety sensors are tampered with and for disabling the AC invertor to conserve power when the wheeled carriage has not been driven for a predetermined period of time.